Photochemical effects during fabrication of holographic gratings in Acrylamide based photopolymer materials

In recent years there has been an increasing interest in holography and its applications. One such application is data storage. Optimising the holographic recording materials is therefore of critical importance in the capacity and clarity of the information stored. Photopolymer materials are practical materials for use as holographic recording media, as they are inexpensive and self-processing. Understanding the photochemical mechanisms present during recording in these materials is crucial in enabling further developments. Obtaining critical material parameters allows improvements of the performance of these materials, such as its spatial frequency response or its environmental stability. This also allows a better understanding of the photochemical processes that occur during the formation of the holographic grating. Our current work, which is presented in this paper deals with two of the processes that occur during holographic grating formation. The first of these is the photochemistry involved in the absorption of the light by the photosensitive dye. We monitor the power of the transmitted beams, which are used for recording the gratings. The second process we concentrate on is the inhibition effect present during grating growth. It has been noted in the literature that there is a slight delay at the start of gating growth. The reason for this delay is due to an inhibition process, which is present to some extent in all photopolymer recordings. The work presented here explains why it occurs. A theoretical model is developed to predict the behaviour of the temporal evolution of the grating. This model has been improved to account for the absorption effects of the material due to the photosensitive dye and the inhibition period, which results in a reduction in the rate of polymerisation.